1. Field
The present application relates to a driving assistance method, program, and driving assistance device.
2. Description of the Related Art
Driving assistance devices are known that prompt lane change when it can be determined that a traffic flow is in a transitional state from a freely flowing state with a low possibility of congestion occurring to a mixed flow state where braking states and acceleration states of vehicles are mixed (see, for example, Japanese Unexamined Patent Application Publication No. 2012-127772.)
Moreover, driving control devices are also known that perform driving control to make vehicle lane changes to high traffic density lanes less liable to occur, so as to make a decrease in inter-vehicle distance less liable to occur as the traffic density for vehicles that have changed lane to a high density lane approaches a critical region (see, for example, Japanese Unexamined Patent. Application Publication No. 2010-035862). In such a driving control device, the occurrence of congestion is suppressed, and congestion is alleviated, by causing a vehicle under driving control in a lane that seems to be becoming congested to change lanes.
The driving assistance devices according to the above technique enable a vehicle to avoid getting caught in congestion in the current lane of travel by moving the vehicle to another lane in cases where there is a high possibility of congestion in the current lane. However, when a vehicle changes lanes, consideration needs to be given to the influence on congestion occurring in the other lanes and to the behavior of other vehicles. When a vehicle decelerates due to vehicles changing lane, this deceleration propagates to a vehicle following, and deceleration also propagates in sequence to another vehicle following that resulting in deceleration of many vehicles traveling in the lane. This deceleration of many vehicles in this lane sometimes causes some vehicles to change lanes, and there are cases where it is not possible to suppress overall congestion across multiple lanes.
Moreover, the driving control devices according to the above technique are sometimes able to change a state toward suppression and alleviation of congestion by entering a lane which seems to be becoming congested. However, due to high traffic volumes at the stage when warning signs of becoming congested are present, sometimes the state is changed toward promoting the occurrence of congestion when frequently changing lanes. Moreover, in order to change the state toward suppression or alleviation of congestion, there is a need for other vehicles driving in a given lane to predict in advance the driving state of a vehicle entering the lane, and to match to the driving state of that vehicle, creating a need to control all the vehicles with a common system.